The interaction of flow and river morphology affects the physical habitat available for any species of interest. This is not a static relationship as the impact of the morphology of the river on the physical habitat available in the river depends on
the flow.

On a fisheries habitat walkover, it would be possible to make a qualitative assessment of the habitat available to a species or life stage of interest. However, this is just a snapshot of the habitat available for a given species or life-stage of interest and it will change with an alteration in discharge or in the physical environment. For example, the installation of a hydropower scheme, river restoration or channel maintenance. Therefore, there is a need in some cases for a predictive tool to help practitioners understand the change in habitat under different conditions.


JHab Post-13
JHab Post-13
JHab Pre-13
JHab Pre-13

Our software team have developed a habitat modelling routine called JHab, which takes modelled depths and velocities and assesses them at a point or region against species-specific habitat requirements. A habitat ‘score’ for each region can then be generated.

There are many well-established methodologies in literature to do this, a classic of the genre being Physical Habitat Simulation (PHABSIM). We have used a fuzzy logic approach, as this treats the depths and velocities as dependent and their effects inter-related. It also incorporates the inherent uncertainty in specifying species or life-stage specific habitat preferences.

JHab has been used on a variety of projects:

Fish pass design studies

Used to assess the passability of an existing weir for fish passage, and to optimise the proposed rock ramp fish passage for fish movement across the operational flow regime.

Hydropower impact assessments

The impact of proposed hydropower schemes on the fish habitat downstream of the weir was assessed by analysing the habitat availability both before and after the installation of the proposed hydropower, across the operation flow regime.

JHab has been used to gain approval for individual schemes and for an Environment Agency Evidence project (SC120077/R1) looking at the wider impacts of hydropower schemes on the ecology downstream of weirs.

River Restoration

Used as part of numerous river restoration design studies to optimise the performance of the proposed scheme on the target species-life stage.


The coupling of JHab to hydraulic modelling results has the following key benefits:

  • Ability to evaluate hydraulic habitat availability across the whole flow regime.
  • Spatial nature of the outputs. For example, the above figure shows the potential changes to brown trout spawning habitat downstream of Goring weir with a proposed (fictional) hydropower scheme. At moderate flows the increased flow facilitated by the hydro down this branch of the Thames improved hydraulic habitat for spawning brown trout (a low habitat score = poor habitat, high habitat score = good habitat). It would however have a negative impact on other brown trout life stages, and so local knowledge remains essential.
  • Ability to get some outputs in a data poor situation.
  • Ability to modify the model topography to understand the impact on habitat availability.

Want to know more?

Email David Mould for more information on hydraulic habitat modelling and hydroeocoogy. You can also visit our Fisheries web page. Find out more about other products our software team have developed on our systems, software and data
web pages

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